1. Field of the Invention
The invention relates to apparatus for use in microwave heating.
2. Description of the Prior Art
Microwave heating has become increasingly popular in the preparation of, particularly, foodstuffs. The microwave energy is radiated within an enclosure from an energy source, such as a magnetron. The waves are radiated and reflected within the enclosure and result in high frequency oscillatory movement of the molecules in a load to cause heating by molecular friction.
The materials being heated absorb energy from the waves in a manner that varies inversely as the distance from the surface to the interior. This variation in loss is usually not sufficient to cause significant change in the coloration from the surface to the interior. For this reason, some technique is desired which will permit higher field concentrations that decrease rapidly with distance to be presented to the surface of the materials being heated. Prior art techniques for controlling the surface coloration have included the incorporation of electric or gas broiling elements in the microwave oven. A coating of a food additive having high energy absorption characteristics as a coating of the outer surfaces has also been suggested. Another example of a prior art teaching is U.S. Pat. No. 3,591,751 issued July 6, 1971 to C. E. Goltsos which discloses a plurality of half-wavelength rods to cause rapid absorption of the energy by the rods. The absorbed heat is then transferred by conduction to a supported load. The heating of the rods by the absorbed energy can lead to problems if the rods are accidentally touched before they are sufficiently cooled.
Another example of a prior art apparatus is described in U.S. Pat. No. 3,857,009 issued Dec. 24, 1974 to G. MacMaster et al. and assigned to the assignee of the present invention. This structure utilizes high and low dielectric constant materials to provide a fringing electric field pattern having a 180.degree. phase differential in close proximity to the exterior surfaces of the load. All of the foregoing prior art teachings are difficult to apply in the case of irregularly contoured loads such as a meat roast or fowl. A need arises, therefore, for microwave apparatus to be utilized for bulky or irregular contoured objects.